Treatment of Vomiting and Gut Disorders

Question 1

Where is vomiting controlled neurally?

Answer 1

2 units in the medulla:

• vomiting (emetic) centre
• chemoreceptor trigger zone

Question 2

Describe the location and function of the vomiting centre

Answer 2

• found mainly in medullary and pontile reticular formation extending into spinal cord
• receives nerve impulses from both vagal and sympathetic nerve fibres
• responds to incoming signals to coordinate emesis

Question 3

Describe the location and function of the chemoreceptor trigger zone

Answer 3

• in area postrema in floor of 4th ventricle
• sensitive to chemical stimuli and is main site of action of drugs that stimulate vomiting
• also involved in mediation of motion sickness

Question 4

What things trigger nausea/vomiting?

Answer 4

• stimulation of sensory nerve endings in stomach and duodenum
• stimulation of vagal sensory endings in pharynx
• drugs or endogenous emetic substances
• disturbances of vestibular apparatus
• various stimuli of sensory nerves of heart and viscera
• rise in intra-cranial pressure
• nauseating smells, repulsive sights, emotional factors
• endocrine factors
• migraine

Question 5

Describe the stages of vomiting

Answer 5

• nausea: feeling of want to vomit. associated with autonomic effects such as salivation, pallor, sweating
• retching: strong involuntary effort to vomit but unproductive
• vomiting: expulsion of gastric contents through mouth

Question 6

What are the types of vomiting?

Answer 6

• projectile vomiting: suggests gastric outlet or upper GI obstruction
• haematemesis: vomiting fresh or altered blood
• early-morning: pregnancy/alcohol/metabolic cause

Question 7

Why are anti-emetic drugs given?

Answer 7

• to stop nausea/vomiting
• only prescribed when cause is known
• treat cause where possible
• if indicated drug is picked according to aetiology of vomiting

Question 8

What are some example indications for anti-emetics?

Answer 8

• severe vomiting during pregnancy
• post-operative nausea and vomiting
• motion sickness
• other vestibular disorders
• induced by cytotoxic chemo
• palliative care
• associated with migraine

Question 9

List the types of anti-emetics?

Answer 9

• antihistamines
• antimuscarines
• dopamine antagonists
• 5HT3 antagonists
• neurokinin 1 receptor antagonists
• synthetic cannabinoids
• steroids
• other neuroleptics

Question 10

What are antihistamines, their use and side effects?

Answer 10

• HI histamine receptor antagonists
• uses include motion sickness and vestibular disorders
• side effects vary and include drowsiness and anti-muscarinic effects (eg. dry mouth)

Question 11

What are some examples of antihistamines and their uses?

Answer 11

• cinnarizine (motion sickness/vestibular disorders)
• cyclizine (motion sickness)
• promethazine (severe morning sickness)

Question 12

What are antimuscarinics and their side effects?

Answer 12

• muscarinic receptor antagonists
• lock muscarinic receptor-mediated impulses from the labyrinth and from visceral afferents
• side effects include constipation, transient bradycardia and dry mouth

Question 13

What is an examples of an antimuscarinic and what its used for?

Answer 13

• hyoscine hydrobromide used in motion sickness

Question 14

What are dopamine antagonists?

Answer 14

• dopamine D2 receptor antagonists
• act centrally as dopamine antagonists on CTZ
• active against CTZ-triggered vomiting but not stomach induced vomiting

Question 15

What are examples of dopamine antagonists?

Answer 15

• phenothiazines (neuropletics/antipsychotics)
• chloropromazine
• prochloroperazine
• domperidone
• metoclopramide

Question 16

What are 5HT3 antagonists and an example

Answer 16

• blockers of 5HT3 receptors in GIT and CNS
• very useful for patients experiencing nausea/vomiting post operatively or on cytotoxic therapy
• eg. ondansetron

Question 17

What are neurokinin 1 receptors and an example

Answer 17

• an adjunct to dexamethasone and a 5HT3 antagonist in preventing nausea/vomiting associated with chemo
• eg. aprepitant

Question 18

What are the synthetic cannabinnoids, the side effects? and an example?

Answer 18

• CB1 receptors
• used for chemo patients unresponsive to conventional anti-emetics
• can cause drowsiness
• nabilone

Question 19

What are the types of laxatives and examples?

Answer 19

• bulk-forming (ispaghula husk)
• stimulant (senna)
• faecal softeners (docusate)
• osmotic laxatives (lactulose)
• peripheral opiod-receptor antagonists (methylnaltrexone bromide)

Question 20

How does diarrhoea affect the GIT?

Answer 20

• increases motility

- decreases absorption of fluid and electrolyes

Question 21

How would you approach treating acute diarrhoea?

Answer 21

• maintain fluid electrolyte balance (oral rehydration prep)
• antimotility drugs
• antispasmodics to reduce smooth muscle tone (eg. hyoscine butylbromide)
• occasionally anti-bacterial agent used

Question 22

What is used to treat chronic diarrhoea with examples?

Answer 22

• anti-motility agents (loperamide)
• absorbents (kaolin)
• bulk forming drugs (ispaghula)

Question 23

What is contained in bile?

Answer 23

• bile salts
• bilirubin
• cholesterol
• lecithin
• plasma electrolytes

Question 24

What medicine can be given to treat gallstones?

Answer 24

• ursodeoxycholic acid to dissolve the stoned

- if mild symptoms

Question 25

How is biliary colic treated?

Answer 25

• with opiods such as morphine as it is very painfully
• if vomiting given parenterally or rectally
• if pain continuous over 24hrs then hospital admission

Question 26

How does colestyramine work and what is it used for?

Answer 26

• forms insoluble complex with bile acids in intestines

- relieves itching associated with partially biliary obstruction and primary biliary cirrhosis